PVD-Deposited Al₂O₃/h-BN Heterostructures for Passive Magnet-Free Optical Isolation: Separating Electronic Kerr and Thermo-Optic Contributions for Aerospace Photonics

Optical isolation is required whenever back-reflected light can destabilize a laser source or contaminate a precision optical measurement. Conventional Faraday isolators are mature and effective, but theirmagnetic elements and polarization optics can impose packaging, electromagnetic-compatibility and mass constraints. This paper develops a testable materials-and-photonics concept based on an asymmetric Al₂O₃/h-BN heterostructure deposited on fused silica. The central hypothesis is that the stack can support a useful intensity-dependent spatial response that can be converted into different forward and reversetransmission conditions.The work deliberately separates two nonlinear pathways. Under ultrashort-pulse excitation, the dominantfast contribution is represented by the electronic Kerr effect, Δn_Kerr = n₂I. Under continuous-waveexcitation, optical absorption can produce a temperature field and a slower thermo-optic contribution,Δn_th = (dn/dT)ΔT. A coupled optical-thermal model is formulated, together with a measurement planbased on forward/reverse transmission, beam-profile analysis, time response and control samples.The manuscript is a research proposal and modelling framework, not a report of completed laboratoryexperiments. Previously stated numerical values for isolation, insertion loss, thermal cycling, radiationexposure and outgassing are therefore not treated as measured results. The proposed environmentalclaims are framed as qualification targets that require experimental verification.